1. Field of the Invention
The present invention relates to an image display control apparatus.
2. Description of Related Art
A known image display control apparatus uses a multi-layer compositing technique to display a single image sheet on a display device (see Patent Documents 1 to 3). More specifically, multiple planes (memory area) are prepared. Data of multiple image sheets (called also layers) are respectively stored in the multiple planes. The stored multiple layers are combined into data of a single image sheet by a plane compositing device. The data of the single image sheet is outputted to the display device, and the single image sheet is displayed on the display device.    Patent Document 1: JP-2008-26450A    Patent Document 2: JP-H9-266551A    Patent Document 3: JP-H7-73278A corresponding to U.S. Pat. No. 5,973,676
In connection with an image display control apparatus utilizing such a multi-layer compositing technique, the inventor of the present application has studied smooth switch of display from one scene to another scene. Discussion will be given below on the smooth switch. Now, examples of the smooth switch are crossfade (called also overlap) and resize. In the crossfade, as shown in FIG. 9, a blend ratio (e.g., display opacity) of an original image 45 is gradually decreased, and a blend ratio of a replacement image 46 is gradually increased. In this manner, the display is changed from the original image 45 to the replacement image 46 via a blend image 47. In the resize, as shown in FIG. 10, an area of the original image 45 on the display screen is gradually decreased and narrowed while an area of the replacement image 46 on the display screen is gradually increased and widened. In this manner, the display is changed from the original image 45 to the replacement image 46 via multiple horizontally-partitioned images 48 and 49.
The above-described smooth switch requires that, for every frame during the smooth switch, N layers for original image data should be generated and stored in the planes and K layers for replacement image data should be generated and stored in the planes. Because of this, processing load and memory band load are disadvantageously huge. Furthermore, if the number of layers (N+K) exceeds the number of planes, it is not possible to combine all of N+K layers into composite image data by using the plane compositing device, and thus, it is necessary to generate in advance a composite layer without using the plane compositing device. As a result, the processing load is further increased.
In connection with the image display control apparatus utilizing the multi-layer compositing technique, the inventor of the present application has also studied display scrolling. Discussion will be given below on the display scrolling. Suppose that a composite image made from multiple layers is scrolled. In this case, every time display position is changed by the scrolling, it is necessary to newly generate layers and store the layers in the planes. Therefore, the processing load and the memory band load are disadvantageously increased.
In addition, for various reasons, the plane compositing device may be reset for a short period of time during display of an image. In this case, the plane compositing device provides an abnormal output; as a result, an abnormal image or nothing is displayed on the display device for the short period. A user may see the abnormal display and may get an idea that the display device is in trouble.